Microbial fuel cells, which convert organic matter into electrical energy by use of microorganisms, mainly include an anode, an ion transfer layer, and a cathode. The anode functions to collect electrons generated when the organic matter is oxidized and decomposed by the microorganisms. The electrons collected in the anode are transferred to the cathode, and consumed through a reduction reaction. The electrons flow across the both electrodes according to a gradient of an oxidation-reduction potential due to a chemical reaction caused in the both electrodes. Hydrogen ions subsidiarily generated by the reaction in the anode pass through the ion transfer layer to reach the cathode. The hydrogen ions react with the electrons and oxygen in the cathode to produce water.
In order to ensure higher output power of microbial fuel cells, apparatuses are required to be scaled up. However, an increase in internal resistance of the fuel cells caused with the increase in size leads to anxiety about a reduction of output power of electrical energy generated.
Non Patent Literature 1 discloses a microbial fuel cell which includes a cathode including a diffusion layer, a catalyst layer, and a metal current collecting layer arrange in order from a gas phase side. Non Patent Literature 1 further discloses that the metal current collecting layer in the cathode is exposed to a liquid phase. According to Non Patent Literature 1, the use of metal as an electrically conductive material can decrease an internal resistance and ensure higher output power in association with an increase in size.